The long-term goal of the proposed research is to analyze the neural mechanisms controlling the expression of arousal in complex behavior. The research will utilize food-induced arousal in Aplysia as a model of arousal in higher animals. The specific aim of the present project is to explore a novel general hypothesis that behavioral arousal is an expression of the action of two types of modulation, both of which serve to improve the efficiency of biting. One type of modulation is extrinsic to the basic sensory-motor circuits that drive behavior. Extrinsic modulation is subject to sensory controls that reflect motivational states. A second type of modulation involves factors intrinsic to the mediating sensory-motor circuits. This type of intrinsic modulation may not be subject to motivational controls, but could serve to fine tune the sensory-motor system so that it can better meet the specific demands of muscle movements. It is not difficult to imagine that malfunction of widespread modulatory systems would have profound effects on behavior and it remains as a distinct possibility that an understanding of these systems in an animal such as Aplysia will contribute to the amelioration of disorders of affect, cognition, and movement.